Numerous types of seals have been designed for use on aircraft to seal against gas leakage at junctions formed between connecting ducts, access panels, or the like. These seals are generally termed "kiss" seals because there are located between flanges that are positioned "face-to-face". Conventionally, a kiss seal is secured to one of the flanges and is pressed against the other flange. Pressurized gas inside the duct produces an outward force, against the membrane of the kiss seal. The function of the seal is to prohibit gas leakage at the unsecured flange.
Known kiss seals suffer from a number of design problems, the most significant of which is how to design a kiss seal that will not leak. If leakage is allowed to occur and continue, in many applications the related structure will vibrate and, as a result, cause failure of the seal, the flanges, or both. To form a tight seal between the kiss seal and adjacent flange surfaces, current designs rely primarily on the seal membrane material stiffness to maintain contact with the flanges. Stiff materials require a large amount of force to mate with the flanges, particularly if the seal is large. More flexible materials result in a poor seal.
The overall shape of a kiss seal also effects its capacity to form a tight bond. During use, linear portions in the seal platform shape will experience longitudinal twisting. This motion can result in flow leakage. Small openings with circular planforms are therefore most desirable, while large openings with rectangular planforms are least desirable. In addition, high temperature and high pressure environments, such as within aircraft engines, are further impediments to good seal performance. Engine duct environments often reach temperatures of 300.degree. F. and pressures of 15 psig.
In addition to the above concerns, a designer must also consider the range of flange-to-flange distances, called flange gaps, that must be accommodated during use. Each kiss seal has a range of compression heights, called its sealing range, within which the seal will be effective. The design goal is to provide a kiss seal with a sealing range that matches the range of anticipated flange gaps. If the expected flange gap range is wide, the sealing range of the kiss seal must be correspondingly wide. If the flange gap is too wide, leakage will occur. The opposite extreme is called bottoming out. Bottoming out occurs when a kiss seal is compressed beyond its design limits. When a kiss seal bottoms out, the seal buckles and folds over onto itself. In aircraft applications, inflight flange motion and assembly tolerances can be quite large, making it particularly important for kiss seals on aircraft to perform well over a wide range of flange gaps.
Therefore, a need exists for a superior kiss seal for use in aircraft applications. The ideal kiss seal should have good sealing capability over a wide range of flange gaps and should require very low compression force to create a seal. The ideal kiss seal should also be able to compress to a small height without bottoming out. The present invention is directed to fulfilling this need.